A malfunction predicting unit is installed to devices comprised in an apparatus providing, for example, a broadcast transmit system to measure the level of a signal input to each devices, and predict occurrence of a malfunction of the apparatus. The malfunction predicting unit prevents malfunction of each device. Conventional malfunction predicting units each incorporate a detector circuit comprising a diode, a capacitor and a comparator. These malfunction predicting units detect the DC component of the input signal using the detector circuit, and compare the detected signal with preset threshold levels using the comparator. If the levels of the detected signal are lower than the threshold levels, it is determined that a malfunction will soon occur in the apparatus.
Recently, high-speed devices have come to be widely used, and hence high-frequency and small-amplitude input signals have come to be used. Under these circumstances, it is difficult to detect input signals by such a detector circuit as mentioned above. Further, the provision of the malfunction predicting unit in the apparatus may disturb the waveform of the input signal, thereby causing malfunction of the device.
Yet further, the conventional malfunction predicting units incorporate a large number of circuit components, such as a diode, a capacitor, a plurality of comparators, and a reference supply. Accordingly, when a variation in signal level is detected, the possibility that the variation is caused by one of the circuit components of the malfunction predicting unit cannot be denied. In addition, since the conventional malfunction predicting units incorporate a large number of circuit components, their circuit scale and manufacturing cost will be inevitably increased.
Jpn. Pat. Appln. KOKAI Publication No. 2001-256736, for example, has proposed a data reproduction apparatus in which the detection performance is enhanced by adjusting the determination level of the detector.